The major objective of this study is to investigate the disposition of the pineal hormone melatonin within the central nervous system. The possible secretion of melatonin into the cerebrospinal fluid of the third ventricle, the metabolism and clearance of radioactively labeled melatonin introduced into the cerebrospinal fluid, the role of choroid plexus and brain tissue in accumulating or transporting melatonin from the CSF and the alteration by sympathetic stimulation of melatonin synthesis, secretion and transport will be investigated. Radioactive melatonin will be infused into the third ventricles of rabbits and cats and clearance of isotope will be studied using double cannula ventricular perfusion technic. Pineal melatonin will be labeled by injection of radioactive indole precursor and the appearance of melatonin in the ventricular perfusate will be compared under control conditions and following cervical sympathetic stimulation. Thin layer chromatography will be used to separate and identify melatonin in the perfusate. In vitro accumulation of melatonin in choroid plexus, hypothalamus and other brain regions will be studied to elucidate regional variations in melatonin uptake, substrate specificity and inhibitor sensitivity.